Rubbers and elastomers of either natural or synthetic origin generally require vulcanization in order to obtain useful elastomeric properties. Before vulcanization, rubbers possess tacky properties and low strength, which make them of little utility except as rubber cements. The optimum elastomeric properties are not attained until the rubber has been subjected to a vulcanization treatment such as by means of heating with sulfur, sulfur compounds, peroxides, or other means. By contrast, thermoplastic elastomers in their "green" or unvulcanized state have been developed which can be utilized to make a wide variety of materials and articles having almost any desired properties. Consequently, such thermoplastic elastomers can be readily molded into useful articles, thereby saving the time and expense of vulcanization as well as retaining numerous properties which are not possessed by vulcanized rubbers or elastomers. A particularly useful group of such thermoplastic elastomers are conjugated diene/vinyl aromatic block copolymers.
It has been known in the past to extend thermoplastic elastomers with petroleum base oils such as naphthenic, aromatic and paraffinic oils in order to reduce costs and to improve the elastomeric properties of certain of the thermoplastic elastomers. Further, it has also been known to add fillers or bodying agents to thermoplastic elastomers in order to reduce the cost of the material and to add bulk and strength to the same. While a vast number of fillers have been suggested in general terms for use in thermoplastic elastomers, there is, in fact, a limited number of such materials which have been successfully used and which are used almost universally. For example, fillers have generally been confined to silicas, carbon blacks, numerous varieties of china clay and whiting or calcium carbonate. However, it has been found that these so-called conventional fillers have a tendency to harden thermoplastic elastomers and limit their uses in articles where flexibility and elasticity are desirable. This is particularly true when large amounts of such fillers are employed. Likewise, the use of excessive amounts of extender oils results in a product which has a tendency to bleed or exude a certain amount of the oil. While the latter is a desirable characteristic in certain uses, in other instances it is highly undesirable.
There are also many methods of forming or molding thermoplastic elastomers such as injection or compression molding, vacuum forming and flow molding, and for applying a coating or sheet of thermoplastic elastomer to woven or non-woven textiles or other substrates, such as calendering or spreading the elastomer on the substrate as a hot melt. These known processes have one or more undesirable features such as requiring extreme pressures, being time-consuming, producing products of poor quality such as poor tear resistance in laminated objects and, in general, undue multiplication of the number of steps required to produce the final product. Because of the reduced pressures required and the reduction in the processing steps necessary, flow molding is an attractive means of forming certain varieties of articles. In a flow molding process, the moldable material in powder, pellet or particle form, or in the form of a sheet is placed in a suitable mold, the mold is closed and the moldable composition heated to a temperature just sufficient to melt and cause flow of the moldable material into the interstices of the mold. Recently, a particularly attractive technique of flow molding has been suggested. In accordance with this procedure the usual flow molding process is carried out except that rather than using radiant heat to melt and cause flow of the moldable material, microwave energy is utilized. Heating with microwave energy has the obvious advantage of substantially shortening the processing time but, in addition, prevents the deleterious effects which often result from heating for extended periods of time.
It would, therefore, be desirable to provide a moldable thermoplastic elastomer composition which retains its property of good flexibility, to provide an article of manufacture having this desirable property and particularly to be able to utilize the above-described, simplified microwave flow molding technique.
It is therefore an object of the present invention to overcome the above-mentioned shortcomings of the prior art.
Another object of the present invention is to provide an improved unvulcanized, moldable composition, a simplified method of molding and an improved molded product.
Another object of the present invention is to provide an improved unvulcanized, moldable composition including a conjugated diene/vinyl aromatic block copolymer.
Another and further object of the present invention is to provide an improved flow molding technique which utilizes microwave energy as a heat source.
Yet another object of the present invention is to provide an unvulcanized, molded article of manufacture having improved flexibility.
Another object of the present invention is to provide an improved unvulcanized, moldable thermoplastic elastomer composition containing a filler material and an extender oil, an improved technique for molding such composition and an improved article of manufacture resulting therefrom.
A further object of the present invention is to provide an improved unvulcanized, modable thermoplastic elastomer composition containing large amounts of filler and extender oil, a simplified technique for molding such composition and an improved article of manufacture produced thereby.
The above and other objects and advantages of the present invention will be apparent from the following detailed description.